1. Field of the Invention
The present invention relates to an information processing apparatus, an information processing method, and a program. In particular, the present invention relates to an information processing apparatus, an information processing method, and a program that enables each user to predict a state of his or her jet-lag syndrome more easily.
2. Description of the Related Art
Since mankind has obtained an aircraft, which is a means of transportation, a phenomenon called jet-lag syndrome (hereinafter, suitably called “jet lag”) has become a big issue. It is unlikely that light-irradiation time suddenly changes as an external environment in nature, and thus jet lag is said to be a phenomenon that has not been experienced by human beings from the viewpoint of biological evolution.
In recent years, there has been a report on a phenomenon in which when an aged rat had suffered from jet lag by suddenly changing light irradiation time, a sudden death occurred in that rat (Lecture material at XI. Congress of the European biological Rhythms Society (EBRS2009), “Symposium 19. Hot topics” S19-1 “Fatal Effects of an immune challenge following repeated phase shifts”, Davidson A J, Castanon-Cervantes O, Ehlen C, Menaker M, Paul K). The same thing might occur to a human being, and thus investigation is urged on what action of jet lag causes death of an individual.
Also, in recent years, researches have revealed that jet lag is a phenomenon that occurs during a period from time when synchronization of expressions of clock genes in a nerve center called a suprachiasmatic nucleus in a brain, which is a central clock of a mammal, is temporarily lost (split into two kinds of synchronization), and to time when the synchronization is obtained again (“An Abrupt Shift in the Day/Night Cycle Causes Desynchrony in the Mammalian Circadian Center”, Mamoru Nagano, Akihito Adachi, Ken-ichi Nakahama, Toru Nakamura, Masako Tamada, Elizabeth Meyer-Bernstein, Amita Sehgal, and Yasufumi Shigeyoshi, The Journal of Neuroscience, Jul. 9, 2003•23(14): 6141-6151•6141).
FIG. 1 is a diagram illustrating right and left suprachiasmatic nuclei.
A suprachiasmatic nucleus (SCN) is a set of neurons situated in a hypothalamus in a brain. From anatomical viewpoint, the suprachiasmatic nucleus is roughly divided into a part having photoreceptors receiving light information from optic neurons and a part not having photoreceptors. The former, the part having photoreceptors, is called a ventrolateral area (Ventrolateral SCN (VLSCN)), and the latter, the part not having photoreceptors, is called a dorsomedial area (Dorsomedial SCN (DMSCN)).
In the case of not having jet lag, both of the expression cycles of the clock genes of the VLSCN neurons and of the clock genes of the DMSCN neurons are kept to be 24 hours in synchronism with a sunshine cycle.
When light irradiation time is suddenly changed in this state, it is observed that the VLSCN clock gene immediately follows a change in the light irradiation time, and the expression of the gene is synchronized with the sunshine cycle after the change (light irradiation cycle). However, in the DMSCN clock gene, the expression is not observed to be in synchronization so quickly as the VLSCN clock gene. As a result, desynchronization occurs between oscillation generated by the VLSCN clock gene and oscillation generated by the DMSCN clock gene.
FIG. 2 is a diagram illustrating observation results of expressions of clock genes of neurons included in a suprachiasmatic nucleus of a rat, a model animal, using a method called “in situ hybridization” by taking a typical clock gene PER1 as an example.
FIG. 2 shows observation results in the case of assuming a flight to the west and delaying a sunshine duration by 10 hours. The horizontal axis shows time, and the vertical axis the number of days. Individual states of suprachiasmatic nucleus show states of expressions for individual two hours. A tinted portion in the suprachiasmatic nucleus is a portion of neurons with expressions of the clock genes.
As shown in a highest row, at 0th day (Day0), the expression is observed while light is irradiated. The expression cycle of the clock gene of the VLSCN neurons and the expression cycle of the clock gene of the DMSCN neurons are synchronized with light irradiation cycle. At the 0-day, light is irradiated from 7 o'clock to 19 o'clock.
As shown in a second row, light is not irradiated from 19 o'clock on the 0th day to 17 o'clock on the first day (Day1) so that the sunshine duration is delayed by 10 hours. Light is irradiated from 17 o'clock on the first day to 5 o'clock. After 5 o'clock on the first day, a state with light irradiation and a state without light irradiation are repeated on a 12-hour cycle.
In this case, for example, as is apparent by the observation results at 23 o'clock on the first day, the expression of the clock genes in VLSCN is observed, whereas the expression is not observed in DMSCN. That is to say, desynchronization occurs between VLSCN and DMSCN. As described above, if light irradiation time is suddenly changed, the expression is observed by immediately following the change in light irradiation time in VLSCN having photoreceptors. However, the expression is not observed in DMSCN having no photoreceptors.
The desynchronized state continues until the 6th day. As shown at a lowest row, on the 7th day, resynchronization occurs between the expression cycle of the clock genes in VLSCN and the expression cycle of the clock genes in DMSCN. On 7th day, the expressions of the clock genes in both VLSCN and DMSCN are observed substantially in synchronism with the light irradiation time.
In the case of assuming a flight to the west and delaying sunshine duration by 10 hours, the expressions of the genes responded to the change in sunshine duration on the 7th day. That is to say, jet lag occurred from the first day to the sixth day.
FIG. 3 is a diagram illustrating observation results of the expression in suprachiasmatic nucleus in the case of assuming a flight to the east and advancing sunshine duration by 6 hours.
As shown in a second row in FIG. 3, light starts to be irradiated from 1 o'clock on the 1st day, and thus light irradiation time is advanced by 6 hours.
In this case, for example, as is apparent by the observation results at 3 o'clock on the first day, the expression of the clock genes in VLSCN is observed, whereas the expression is not observed in DMSCN. Thus, desynchronization occurs between VLSCN and DMSCN. The desynchronized state continues until the 12th day. As shown at a lowest row, on the 13th day, resynchronization occurs between the expression cycle of the clock genes in VLSCN and the expression cycle of the clock genes in DMSCN.
As shown in FIG. 3, in the case of assuming a flight to the east and advancing sunshine duration by 6 hours, the expressions of the genes responded to the change in sunshine duration on the 13th day. That is to say, jet lag occurred from the first day to the twelfth day.
As experienced by overseas travel, recovery time from jet lag is different in the case of a flight to the west (in the case of delaying time) and in the case of a flight to the east (in the case of advancing time). Actually, this phenomenon quite matches the period from time when desynchronization occurs between the above-described clock genes in a suprachiasmatic nucleus to time when resynchronization occurs. The observation results like this is described in the non-patent document, “An Abrupt Shift in the Day/Night Cycle Causes Desynchrony in the Mammalian Circadian Center”, Mamoru Nagano, Akihito Adachi, Ken-ichi Nakahama, Toru Nakamura, Masako Tamada, Elizabeth Meyer-Bernstein, Amita Sehgal, and Yasufumi Shigeyoshi, The Journal of Neuroscience, Jul. 9, 2003•23(14):6141-6151•6141).
It has been revealed that jet lag is a phenomenon that occurs during an unstable period from time when desynchronization occurs between the expressions of two different kinds of clock genes in a suprachiasmatic nucleus to time when resynchronization occurs. However, it has not been figured out why time periods necessary for resynchronization are different between the case of advancing time and the case of delaying time.
A study is made for modeling in a non-patent document, “Mathematical model expressing SCN at the time of jet lag”, Takeshi Asakawa, Satoshi Koinuma, Mamoru Nagano, and Yasufumi Shigeyoshi, poster presentation “Second Japanese society for quantitative biology 2010”, as follows. A VLSCN neuron and a DMSCN neuron are expressed as oscillators that are mutually in cooperation with each other, and the clock genes of the VLSCN and DMSCN neuron groups are interpreted as a dissipative system in order to model the system. It is noted that the cause for one neuron in a suprachiasmatic nucleus producing limit-cycle oscillation is the fact that a clock-gene network itself constitutes a negative feedback loop (refer to “A model for circadian oscillation in the Drosophila period protein (PER)”, Goldbeter A., Proc. R. Soc. London Ser. B261, 391-324).